Pendulum damping device for elevation meters



Oct. 14, 1952 J E|$| ER 2,613,449

PENDULUM DAMPING DEVICE FOR ELEVATION METERS Filed Aug. 51, 1945 2 SHEETSSHEET l INVENTOR. Joseph D. Ejs/er BY Oct. 14, 1952 J. D. EISLER 2,513,449

PENDULUM DAMPING DEVICE FOR ELEVATION METERS Filed Aug. 31, 1945 2 SHEETSSHEET 2 4 19 35 o I 6 g if 25 Cenfer of gravity of disk pendulum I INVENTOR: Joseph D. EJ3161- B Y I .Affornqy Patented Oct. 14, 1952 ELEVATION METERS Joseph D. Eisle r, Tulsa, Okla., assignor to Stanclind Oil and Gas Company, Tulsa, Okla., a corporation ofDelaware Application-August 31, 1945, Serial No. 613,824

Claims. (01. 33 -220) This invention pertains to the art of damping of an oscillatingmember. More particularly, it pertains to the art of damping a pendulum where such pendulum is supported on an oscillating or moving vehicle. 'Ihefmost important application is therefore in the arts of gradient and differential elevation determination in which a pendulum is employed as a reierence'to obtain the slope of a path over which a vehicle travels.

It is well known thatfafreely suspended pendulum will" oscillate wlien the pendulum support is accelerated or decelerated. It is also well known that a pendulumywhich is carried by a moving vehicle will; tend to oscillate irrespective of ordinary accelerations or deceleraticns of the support along thepatlifiof the vehicle. In other words, the pendulumma'y be caused to oscillate even by an acceleration normal to the path over which the vehicle is traveling, especially when such acceleration happens at an instant when a line through the center of gravity of the pendulum and its center of suspension is not normal tothepath. f

Various means'have been proposed to compensate for the-displacement of apendulum from the vertical, 1. e'., fr: om anoint where a line through the center offgravity of the pendulum and its axis of rotation is absolutely vertical, due to accelerations and decelerations of the support in the direction of travel. Suchjcompensation has in general proved Satisfactory for the specified purpose. I have found, however, that" even with compensation for acceleration-anddeceleration along the path of the vehiclebarrying the pendulum, due to vertical accelerations and decelerations or other fluctuations of thevehicle, the pendulum, particularly a pendulum mounted on low friction pivots, will tend to oscillate about its axis of rotation. It is necessary to damp such oscillations, particularly on a gradiometer or elevation meter, so that a plot of the path will truly represent the path and so that a follower mechanism will be able to follow the excursion of the pendulum.

It is desirable to damp the pendulum internally, i. e., without the use of external forces.

Internal damping, however, appears impractical so external damping-has .been employed. Damp or damping as the terms are used herein refers to the resistance forces, such as accomp-any eddy currents irra metallic member as it is moved in a magnetic field, applied to a vibrating member, which resistance forces are proportional to the relative velocity between the vibrating member and the restraining member. The terms'specificall include'all cases in whichappreciable work or energy is dissipated and the vibrations are diminished progressively. 'Various means have been proposed to. damplexternally an "oscillating member on a traveling support. -For example, it has been proposed to mount a metallic disk on mounted on a moving support.

the axis of the pendulum. Permanent magnets are then. mounted on the support and coact with said disk to damp electromagnetically the oscillations of the pendulum. It has also been proposed to place friction members on the pendulum which coact with the support to damp the oscillations of the pendulum. Furthermore, it has been proposed to'suspend the pendulum in a viscous fluid to damp the oscillations thereof. 'All of these proposals, however, have the same characteristic, viz., the tendenc for the support to rotate the pendulum, which tends to make their use impractical in situations where it is necessary that the pendulum be unaffected by motions of the support. Thus, with the first-mentioned electromagnetic means a rotational oscillation of the support about the axis of suspension of the pendulum would tend to rotate the pendulum, and in applications such as gradiometers or elevation meters this rotational effect on the pendulum introduces errors which are undesirable, particularly when an accurate survey is required.

It is therefore an object of this invention to provide an improved pendulum damping means which will as nearly as practical be equivalent to an internal damping means. It is a further objeot of this invention to provide a dynamic damping means for a pendulum. A still-more specific object of thisinvention is to provide dynamic damping means for a pendulum whereby the pendulum will not be affectedby oscillations of the support. A still further object of this invention is 'to provide an electromagnetic damping means for a pendulum used on an elevation meter whereby the rotational oscillations oi the vehicle carrying the pendulum about the pendulum will not be transmitted to the pendulum. Other ob jects and advantages of the invention will become apparent as the description thereof proceeds.

This invention mav be described generally, therefore," as an a paratus for damping the oscillations of apendulum mounted on atraveling support in which the damping means is rotatably mounted on the support on the axis of the pendulum whereby rotation of the support about the axis of support of the pendulum will not be transmitted to the pendulum.

The accompanying drawings are illustrations of certain embodiments of my invention andare included for the purpose of explaining the operation of the invention as applied to'an elevation meter. However, the invention finds application in other arts in which an oscillating member is In these drawings which form a part ofthis specification and areto beread in conjunction therewith, the same referencenumerals in the various figures refer to ,the same or corresponding parts. In these figuresz, Figure l :is a diagram of the geometric quantito photoelectric cell 2 I.

ties involved in the explanation of this invention;

Figure 2. is an oblique view creche-embodiment of an elevation'meter in which dynamic damping means in accordance with this invention are employed in conjunction with a disk pendulum;

Figure 3 is an oblique view of an alternative embodiment of a dynamic pendulum dam-ping means; and

Figure 4 is a diagram used in the explanation of one feature of this invention. I

In Figure 1 a vehicle II is shown on a certain path I2 between points A and B, between which points the difference in elevation is to-be determined. This difference in elevation is the distance D as shown. The total length of the path from A to B is a certain distance S (not shown). Angle represents the angle of inclination of. the path atany point 0 along the path-Ki -It.is apparent that the incremental difference in ele vation dh between point C and; a point an incremental distanceds from C is; given by theequadh=ds sin. 0 (1) Thetotal difference in elevation D between points Aand-B is given by the equation B D=f sin dds (2) -In other words, the difierence in'elevation between points A and B is the integralof the product of each increment of distance ds times the sine of the corresponding angle of inclination '0. It is to be noted that in this derivation it makes no difference what the horizontal; projection of the path Sis. That is, if the vehicle travels from= A to B over any path, straight or, curved, the .total difference in elevation'D betweenthe two points A and B must be the same. If ,a pendulum I3 is mounted on vehicle I I, the angle of inclination of :a line perpendicular to-thebed of the vehicle relative to the pendulum is-given by theangle 0, which is the angle of inclination of the path at that point C.

which is mounted on torsion fiber I I-at a point on the disk some distance-from the-center of gravity of the disk. The pendulum may be pivotedcn a low friction bearing, ,e.-g.,-:a jeweled hearing. I prefer, however a torsion fiber I4 which suspends the pendulum betweenthetwo supports I5-and I6 that are in turn carried-by the vehicle I I. A smallmirror I1 is mounted. on the axis of the pendulum I3. LightJfrom-a uniform source, such as lamp I-8, which is energized bya-battery I9, is focusedonmi-rror I I and 'refiected towards a photoelectric-cell M. A light shield v22 having a narrow slot- 23 in the top thereof directs a narrow beam of light from lamp I8 The lamp I Sand photoelectric cell 2I are so positioned and theelasticity of torsion fiber- I4 is so adjusted that the amount oilight which reaches the photoelectric cell is directly related to the angle 0 asindicated in Figure 1. Preferably the lamp and photoelectric cell are positioned so that when the pathof the vehicle is horizontal, one-half of the narrow beam of light enters the lower portion of the photoelectric cell. An upward inclination of the path I2 when the instrument is traveling .away from the observer then increases the amount of light entering the photoelectric cell, and likewise the downward inclination of the path I2 decreases theamount of light entering the photo- '..jelectric cell. Accordingly the direct current out- .vehicle. .121 ispropo'rtional .to the velocity of the vehicle .in;.thef direction of travel. This output voltage put of the photoelectric cell is directly related at all times to the angle of inclination of the vehicle II.

" The-outputof the photoelectric cell 2I is amplified' by an amplifier 24 which produces an output current in the leads 25 proportional to the inclination of the path at the point under consid- 'e:ation. This-current is impressed across the current coils of an indicating or recording watthour meter 26. -An electric generator, preferably a direct; current generator 21, is coupled either directly or by a linkage means to a wheel of the The output voltage of this generator in. which..E..is the voltage across the potential I coils, I isthe current in the current coils, and dt is. an, increment of..time. In this case the differ- .ence in-time (tz-ti) is the time required to travel the path. I2. asindicated in Figure 1 between the two ,points A,,and B. -The voltage E is propor- ..tional to the velocity of the vehicle along the v,path I2 and, hence, isdgivenlby the equation l. d han -jwhere Kiis .a. constant of; proportionality. The

current I is proportional to the illumination of the photoelectric cell 2|. But for the torsional force. in thetorsion fiber I4, with the arrange- ,ment showninFigure 2 this illumination is related ,to twice the angle of inclination 0 as is obvious fromthegeometry of the construction, andtherefore the equation for the current I would be where IQ is :aconstant of proportionality. By

,selecting ,a.=torsion-fiber I4 having a restoring torquewhichrwill cause the pendulum I3 to rotate throughcan angle of /20 the current I producedbyphotoelectric cell 2| becomes I='Kz0 (5) Substituting the values for E and I from the Equations igand .5, in Equation 3 the watt-hour meter reading It becomes Fora-angles of inclination: up to and including 10 thesineofatheangle is substantially equal to the angle-inv-radians. ;A:self-propelled vehicle is generally limited ;to slopes of this order.

portional to twice the angle of inclinationof the vehicle -I-I may 'be made substantially proportional to the sine ofthe angle of inclination of the vehicle. Any departure from the true sine of 26 can be substituted for the difference in elevation D, and by combining the constants K1 and K2 into a single constant K Equation 2 becomes The apparatus containing a photoelectric cell as above described is not adapted toindicate negative angles. That is, the photoelectric" cell produces only positive current. Consequently, in

. the measurement of angles with, the photoelectric cell, the angles are always measured asposit ive current, the photoelectric cell being so con structed and arranged that the angle of zero-output is greater than anyslope over which the vehicle carrying the elevation meter will pass. For example,.the lamp i8, mirror I! and photoelectric cell 2| might be positioned relative to each other such that when thevehicle is-traveling downgrade at an angle of, say, 20, the output of the photoelectric cell is zero. Under these conditions, when the path is level, the photoelectric cell would have a positive current output of a given value and when the elevation meter is proceeding on the path with an upgrade of, say, 20, the photoelectric cell output is still positive and quantitatively twice the aforesaid Value when the path is level. Thus it will be apparent-that an elevation meter'employed in an integrating device of the type described in connection-with the embodiment of this invention shown in Figure 2 and mounted on a moving vehicle, must be calibrated to obtain an instrument constant. This constant would be the reading of the watt-hour meter had the instrument traveled on a level path between the same points. In order to obtain the actual elevation between two points the instrument constant would therefore be subtracted from the watt-hour meter reading R. as set out below in Equation 8. I, therefore, provide'means for measuring the distance S between stations A and B and determine the true difference in elevation dh between the two stations A and B from the following equation,

dh=R--K3S (8) angle of inclination, and means for integrating the products of this multiplication between'points A and B at the endsof the surveyed path.

It will be apparent to those; skilled in the art that the pendulum 13 will tend to oscillate about suspension fiber l4 whenever the vehicle l l tends to rotate about the same point, as for example, when a front wheel 28 or a rear wheel 29 is raised or lowered with respect to the other. That is, suspension fiber I4 having some restoring torque will tend to rotate pendulum I3 whenever the supports i5 and I6 rotate about the fiber. Oscil lations thus induced in pendulum l3 tend to continue whether or not the pendulum I3 is supported on a torsion fiber or any other low-friction pivot. In the devices of the prior art, damping means have been attached directly to the vehicle I l or to the supports I 5 and I6 as explained above. Such a construction tends to cause undesirable inaccuracies due to the fact that any rotation of the damping means about the center of rotation of the pendulum tends to rotate the Y pendulum. In accordance with my invention a instruments of this nature.

portion of the damping means is rotatably mounted on the vehicle. That portion which is thus mounted has a very high inertia, i. e., an inertia substantially greater than the inertia of the system being damped, and a very low frictional mounting whereby it will tend to remain in the same position, especially on high frequency oscillations such as cause the most trouble in I have shown a damping means in which an electromagnetic means, preferably high inertia permanent magnets 31, are associated or coact directly with the disk pendulum l 3. It should, however, be pointed out here that this invention is not limited to the placing of these elements in the position shown;

neither is it limited to the use of a disk pendulum, for the disk may beonly remotely connected with the pendulum or any other oscillating" member. Also, the magnetic elements may be connected to or constitute the oscillating member, and the high inertia element may be connected to or constitutethe disk or any other plate. Permanent magnets 3l are mounted'on a framework 33 whichhas a tubular axle 34.' This axle is made tub'ular so that the pendulum suspension torsion fiber I4 may pass through it as indicated. Framework 33" is in turn rotatably mounted on the support l6. Low friction bearings 35 are preferably employed to decrease the tendency of the'permanentmagnets3l to rotate with-support l6. i H

The permanent magnets 3| maytake any convenient form; however, I prefer that the pole pieces 38 be shaped and placed as indicated. That is, I prefer that the magnetic flux in the gap between the poles of the magnet be concentrated and elongated with the longer axis in a radial direction. The theory of operation for this improvement is not clearly known. However, one explanation may be made on the following basis.

Inasmuch as the arrangement of elements shown in the electromagnetic damping means is in effect a combination generator-motor in which the current I flowing in the imaginary winding abcda (see Fig. 4) and the magnetic flux 5 is the where E is the voltage output of an electric generator, T is the turning force exerted by each of the damping means, K7 is the product of K5 and K6, constants of proportionality, Us the eirective length of the pole pieces perpendicular to the relative motion of the plate and magnets, w isthe angular velocity of the pendulum with reference'to the magnets, r is the distance radially from the axis of the disk to the center of the imaginary current path abcda, and R is the total "resistance of'the' disk to the-sow ofcurrent in the imaginary current path abcda.

Since R a'bcd llp Equation 9 becomes fl= (1,0) abcda p eifective length of the pole pieces Z perpendicular tothe relative motion of the-plate and magnet increases with respect to the total. length of the imaginary current path.

I have found also that thezpole pieces should be spaced a substantial distance a: from the edge of the disk to increase efiectively the quantity 2.

In Figure 3 I have shown an alternative embodiment in which the pendulum l3 and the disks 3'! are separated. The pendulum l 3 and the disks 31 are, however, rigidly mounted on the same axle 38 whichv may be suspended on torsion fiber M or any other low friction pivot. Theprinciple of operation of this embodiment is substantially the same as the principle of operation of the embodiment shown in Figure 2 I-Iereagain-the high inertiamembers 3| are rotatably mounted on supports l5 and it so that any rotation of these supports about the =center.of rotation of the pendulum [3 will not tend to rotate the high inertia members. While two disks 3'! are'shown for symmetry in connection with this embodiment, it will be apparent to those skilled in the art that either disk may be used alone without departingfrom the spirit of this invention.

While I have described my invention with particular reference to an elevation meter application and with particular reference to electromagnetic damping means, it is to be understood that this inventionis not to be limited to these embodiments, but it is only to be limited by the scope of the appended claims.

I claim: r

1. In a gradiometer a dynamic damping apparatus for a pendulum suspended on torsion fibers between two supports comprising an electrical conducting plate'associated with said pendulum,a balanced ma'gnetic means including a magnet mounted to'rotate freely on a pendulum support with the axis of rotation of said pendulum and said plate 'coincidentahsaid plate being disposed in the magnetic field of said magnet whereby eddy currents are induced into said plate to damp the oscillations of said pendulum, said magnet having an oblong pole piece, and said oblong pole piece being disposed with its longer axis perpendicular to the relative motion between said plate and said magnet.

2. In a leveling device employing an eddy current damped metallic disk pendulum suspended on torsion fibers between two supports as a reference to determine grade, the improvement comprising mounting at least one high inertia balanced magnetic structure to rotate freely on comprising a high one 'of s aidpridiiliimfsupports, said pendulum efidsamfstructure rotating about the same axis and-said 'structurebeingadapted to produce a iriagne'tic field "through said pe'ndulum' whereby high freque'ncy oscillation of said pendulum support aboutsaid axi wnrnet be transmitted by "said structure to'said pendulum.

3. In an elevation meter including a pendulum suspended on torsion fibers between two supports the results of said multiplication, and means to damp the high frequency oscillations of said pendulum, the improvement in said last named 'means' comprising high inertia balanced magnets mounted to rotate freely on said supports whereby high frequency oscillation of said supports about said axis will not be transmitteted to said pendulum.

4. In a gradi'omet'er a dynamic damping means for 'an electrical conducting disk pendulum suspended on torsion fibers between two supports inertia magnetic means mounted 'on one of saidsupports and freely rotatable cn'the axis of rotation of said pendu- 'lum,"said pendulum being disposed in the magnetic field of's'ai'd high inertia magnetic means, whereby eddy currents are introduced in said pe'ndulum'to damp the oscillations thereof.

5. In a 'gradiometer employing a metallic disc pendulum suspended on torsion fibers between two'supports as a reference to determine slope, a

"balanced, high-inertia, magnetic means rotatably mounted on one of said supports, the axis of rotation of said pendulum and said balanced, highinertia, magnetic means being coincidental, and

' said'metallic disc pendulum being disposed in the magnetic: field or" said high-inertia, magnetic 'means, whereby eddy currents are introduced into said metallic disc pendulum to damp high-frequency oscillations thereof and whereby pendulum is free from frictional forces.

JOSEPH D. EISLER.

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